The tension/relaxation thing, I don't know where you got that because that's something I got from Systema guys. I've rolled with Vlad and he did the get my body to tense up in ways that would allow me to be easily put down. I don't know if this is the same as aiki though, unless you can explain more.
Keith I like that sandbag analogy! It easily describes what I'm trying to say, heh.
I'd seen/felt it in various places, Toby, Mike and Ikeda, but like a lot of this stuff it didn't really come together in any measurable way until I started putting in enough time to be able to play with it more myself, feel it and then noodle things out in my head. Most of my time in aikido these days are spent playing with that basic idea and exploring the results/reactions in uke, which is how I think it's supposed to be. We try to avoid the whole "going through the motions" thing in our org and we have plenty of people who enjoy being hard to move and It's really fascinating to see how even a little bit of body skill can subtly influence a larger/stronger person who simply isn't connected, much less trying to incorporate the other aspects of IS into their movement. On the flip side, it's also interesting to see how easily it is, at least at my level, to have it not work at all for me when one of those aspects are neglected.
As far as calling it aiki, I think it depends on how its done. When done in the way we're talking about, using the body skills we're talking about, I wouldn't hesitate to call it that. Especially considering that it seems to conform to the common demos we see of aiki, which is getting under uke for kuzushi. Though I reserve the right to change my opinion at any time